1. Field of the Invention
This invention relates to an apparatus for controlling the vibration of a vehicle.
2. Description of the Prior Art
In a conventional apparatus for controlling the vibration of a vehicle, which is as known from, for example, Japanese Patent Laid-open No. 11954/1980 (corresponding to U.K. Pat. No. 2025572), the vibratory acceleration of a car body is detected, and the result of the detection is compensated so as to reduce the vibration of the car body, and a fluid pressure acting means which is provided between the car body and is operated in accordance with the result of the compensation, i.e. a vibration suppressing instruction to thereby suppress the relative vibration between the car body and truck. The fluid pressure acting means generally consists, when compressed air is used as an operating liquid, of a double-acting air cylinder. An air servo valve is used as a fluid controller which is adapted to control the compressed air supplied to the double-acting air cylinder. The output characteristics of the operational power of the double-acting air cylinder include saturation characteristics so as to secure safety when an abnormal phenomenon occurs due to the erroneous operation of the acceleration detecting means and various types of compensating means or the controllability of various types of control means. The saturation characteristics of the double-acting air cylinder can be obtained by, for example, providing the air servo valve with the pressure-flow rate characteristics shown in FIGS. 1 and 2. An example, in which the lateral vibration of a car body is reduced by the doubled-acting cylinder and control means therefor, will now be described. When a vehicle runs on a curved railroad at a high speed, i.e., at such a speed that causes the surplus centrifugal acceleration to be applied to the car body, the surplus centrifugal acceleration is applied from the car body in the lateral direction toward an outer rail on the curved railroad. Accordingly, in the vibration control unit consisting of the double-acting air cylinder and control means, the acceleration detecting means detects, in accordance with its operational principle, the surplus centrifugal acceleration, which is applied in the lateral direction of the car body, as the centripetal acceleration. The results of the detection by this acceleration detecting means are as shown in FIG. 3. In the results shown in FIG. 3 of the detection by the acceleration detecting means, the acceleration, which causes the car body to be shifted steadily in the lateral direction with respect to the chassis, i.e. a drift component D is shown as the centripetal acceleration .alpha. and is the displacement relatively generated between the car body and the truck. Therefore, the double-acting air cylinder which is controlled in accordance with the results of the detection provided by the acceleration detecting means is moved so as to displace the car body toward the outer rail. During this time, the surplus centrifugal acceleration working on the car body is high as compared with the acceleration based on a lateral vibration component occurring while the vehicle runs straight, so that the double-acting air cylinder is operated so as to move the car body to the side of the outer rail up to the limit of the saturation characteristics thereof. Consequently, the car body is displaced to the side of the outer rail due to the operational force of the double-acting air cylinder and the surplus centrifugal acceleration to be pressed against a lateral movement stopper which is provided so as to restrict the lateral movement of the car body with respect to the truck in a predetermined range. When the car body is in this condition, the double-acting air cylinder is in a saturation region, and the vibration-reducing functions thereof do not work. Moreover, since the car body is pressed against the lateral movement stopper, the functions of the double-acting air cylinder of reducing the lateral vibration between the car body and truck lower. In addition, there is the possibility that the degree of comfort of a ride on the car body is impaired due to the impulsive lateral acceleration based on the vibratory force transmitted from the railroad to the car body via the truck.
When the vehicle runs on a curved railroad at a high speed, a vertical drift component due to the rolling of the car body occurs in the vertical vibration thereof, so that the same problems mentioned above occur.
Various measures for eliminating such problems may be imagined, which include a measure in which the results of the detection carried out by the car body acceleration detecting means are passed through a high-pass filter and then used for a control operation. However, the variations of these results have an influence even upon the control characteristics based on the results of the detection of regular vibratory acceleration, and good results cannot actually be obtained.